From my understanding from business friends and small business...

From my understanding from business friends and small business network who have switched from Tyro to Square, they have enjoyed the seamless out of the box POS setup with Square and are quite happy with a larger fee. Remember, it's only approx 0.4 basis points they pay for better reliability. These 'micro' merchants are definitely in the $20k pm turnover.
Interestingly, the mobile coffee van is very near the top when they do events.
In short, I think the segment is underestimated which is why Square has flown under the radar with the initial visibility from the part time market traders but one network user is a commercial plumber and he uses it immediately after a job... saves billing and collections time.
I also understand Tyro intends to or has now delink the KYC requirement to sign up as they bundled the bank account as a mandatory offering that put off a lot of customers who just wanted eftpos.